U.S. patent number 4,893,918 [Application Number 07/141,622] was granted by the patent office on 1990-01-16 for contact or intraocular lens from lightly crosslinked polymer or copolymer of 2-hydroxyethyl methacrylate and a method for producing thereof.
This patent grant is currently assigned to Ceskoslovenska Akademie Ved. Invention is credited to Zuzna Krcova, Jiri Sulc.
United States Patent |
4,893,918 |
Sulc , et al. |
January 16, 1990 |
Contact or intraocular lens from lightly crosslinked polymer or
copolymer of 2-hydroxyethyl methacrylate and a method for producing
thereof
Abstract
Contact lens or intraocular lens from lightly crosslinked
polymer of 2-hydroxyethyl methacrylate or from such its copolymer,
where the 2-hydroxyethyl methacrylate component prevails over the
second nonhydrophilic component, which contains a hydrophilic
swellable transparent surface layer and an inner portion of lower
swellability than the surface layer, whereby the swellability of
the surface layer decreases continuously from the exterior of the
surface layer towards the inner portion to the swellability level
of the inner portion. The swellability of the exterior of the
surface layer is at the surface layer of up to 98% and the
thickness of the surface layer is at utmost 100 .mu.m. The finally
shaped lense is treated with an alkaline reacting solution of a
salt, in which the lens does not swell and the lens is then freed
of all soluble substances by washing.
Inventors: |
Sulc; Jiri (Prague,
CS), Krcova; Zuzna (Prague, CS) |
Assignee: |
Ceskoslovenska Akademie Ved
(Prague, CS)
|
Family
ID: |
5333879 |
Appl.
No.: |
07/141,622 |
Filed: |
January 6, 1988 |
Foreign Application Priority Data
Current U.S.
Class: |
351/159.33 |
Current CPC
Class: |
G02B
1/043 (20130101); G02C 7/04 (20130101); G02B
1/043 (20130101); C08L 33/14 (20130101) |
Current International
Class: |
G02C
7/04 (20060101); G02B 1/04 (20060101); G02C
007/04 () |
Field of
Search: |
;351/16H,16R |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Arnold; Bruce Y.
Assistant Examiner: Callaghan; Terry S.
Attorney, Agent or Firm: Leydig, Voit & Mayer
Claims
We claim:
1. A method for producing a contact or intraocular lens comprising
treating a shaped lens comprised of a lightly crosslinked
2-hydroxyethyl methacrylate polymer or a lightly crosslinked
2-hydroxyethyl methacrylate copolymer in which at least 50 percent
of the monomer units are 2-hydroxyethyl methacrylate units, and the
remaining monomer units are of non-hydrophilic comonomer, with an
alkaline-reacting solution of a salt which will not cause the lens
to swell for a time sufficient to form a hydrophilic-swellable and
transparent partially saponified portion on said lens, and
subsequently freeing the lens of all soluble substances by
washing.
2. The method for producing a contact or intraocular lens according
to claim 1, wherein the swellability of the lens continuously
decreases from the surface toward an inner non-saponified portion
until the swellability is equal to that of the inner non-saponified
portion.
3. The method of producing a contact or intraocular lens according
to claim 2, wherein the swellability of the partially saponified
portion of the lens is up to 98 percent and the approximate depth
at which the swellability equals that of the non-saponified inner
portion is not greater than 100 microns.
Description
The invention pertains to hydrogel contact lens or intraocular lens
from lightly crosslinked polymers of 2-hydroxyethyl methacrylate,
or from such lightly crosslinked copolymers of 2-hydroxyethyl
methacrylate where the 2-hydroxyethyl methacrylate units prevail
over the units of other virtually non-hydrophilic monomers, and to
a method for their production.
It is known that hydrogel contact lenses and intraocular lenses are
best tolerated if they are softer than the living tissue against
which they lean. However, the very soft lenses with the swelling
capacity 60 to 90% of water have a low strength and are readily
damaged by handling. The swelling capacity is to be understood here
to be the content of water at equilibrium swelling at 20.degree. C.
In addition, the refractive index of light decreases considerably
with the increasing content of water and the lenses made from these
hydrogels need to be relatively thicker for higher dioptric values.
Consequently, the advantage of a better penetration of atmospheric
oxygen to cornea is again lost in part because the diffusion path
is longer.
For the above purposes, the polymer of 2-hydroxyethyl methacrylate
(HEMA) crosslinked with less than one percent of ethylene glycol
dimethacrylate is hitherto mostly used. It has very good optical
properties and sufficient mechanical properties, but the lenses
made of it are very well tolerated only if they are perfectly
smooth, because the material is harder than the surface of cornea.
It was proposed therefore to partly saponify some parts of the
inner surface of lens with alkaline hydroxide. The saponified
places become strongly swellable, does not irritate the cornea, and
take the lens away from the surface of cornea thus enabling a free
circulation of tears and a sufficient supply of oxygen which is
dissol ved in tear liquid to the surface of the eye.
However, the local strong swelling is unsuitable for some designs
of lenses, above all for intraocular, lenses. The invention relates
to lenses which possess a softening of the surface layer of the
lens, and if desired the inner portion, this being accomplished by
treating the lens so as to form a very thin layer of strongly
swollen soft gel, whereas the optical properties of poly-HEMA are
retained.
The subject of invention is a contact lens, or an intraocular lens,
from the lightly crosslinked polymer of 2-hydroxyethyl
methacrylate, or from such a lightly crosslinked copolymer where
the 2-hydroxyethyl methacrylate component prevails over the other
nonhydrophilic component, which is characterized in that it
contains a hydrophilic swellable transparent surface layer and an
inner portion of lower swellability than the surface layer, whereby
the swellability of the surface layer decreases continuously from
the exterior of the surface layer towards the inner portion to the
swellability level of the inner portion. The swellability of the
surface layer is at its exterior of up to 98% and the thickness of
the surface layer is at utmost 100 .mu.m. The contact lens or
intraocular lens according to the invention is characterized in
that the surface layer is formed by alkaline hydrolysis.
The copolymer containing at least 50% of 2-hydroxyethyl
methacrylate units and at utmost 50% units of a nonhydrophilic
monomer comprising C.sub.1 to C.sub.6 -alkyl esters of methacrylic
and acrylic acid, acrylonitrile, methacrylonitrile, vinyl esters of
aliphatic caroxylic acids, styrene, and vinylcarbazole may be
advantageously used.
The method for production of contact lenses or intraocular lenses
according to the invention comprises treating of a finally shaped
lens by an alkaline reacting solution of salt in which the lens
does not swell and the subsequent removing of all soluble
substances from the lens by washing. However, the procedure where
the lens in part swollen with water or aqueous solution is immersed
into a warm, alkaline reacting solution of salt may be also
applied.
The procedure according to the invention comprises partial
saponification of a very thin surface layer of poly-HEMA using
concentrated solutions of salts in which poly-HEMA swells only
slightly or not at all and which have an alkaline reaction as such
or with addition of a strongly alkaline compound, above all
alkaline hydroxide. The finally shaped lenses are immersed into
these warm solutions for a short time, for example, for several
minutes, then are freed of salts and alkaline substances by washing
and immersion into physiologic saline. The lens may be before
immersion into the salt solution either completely unswollen in the
form of xerogel or may exhibit an arbitrary degree of swelling. It
proved suitable to use the lenses swollen with water or other
liquid to equilibrium for this processing without an undesirable
gradient occurring between both materials, i.e. between the
partially hydrolyzed surface layer and the bulk mass of lens. The
very thin strongly swollen surface layer adheres very well to the
lens even without a perceptible transition gradient which is in the
case of thicker surface layers necessary. Thickness of the
partially saponified layer in the completely swollen state is about
10 to 100 .mu.m.
It was also revealed in a striking way, that such a thin layer
removes irritation of cornea and, in addition to this, levels the
unevenness of lens which are very small in the swollen state and
visible only with a microscope, thus increasing the comfort of
patient very much.
Numerous salts can be used which are soluble in water to
concentrated solutions in which poly-HEMA does not swell and, on
the contrary, deswells if it is swollen. Such salts are, for
example, alkaline salts of strong mineral acids, as sodium sulfate
or phosphate (normal trisodium phosphate), alkali metal carbonates
and hydrogencarbonates, alkaline salts of some organic acids, for
example, sodium acetate, and others. Also mixtures of two or more
salts can be employed. Applicable also are the salts of alkaline
earth metals, e.g. calcium or magnesium chloride.
To attain the alkaline reaction, an arbitary strong base, e.g.
sodium hydroxide, is added. The salts, which are strongly alkaline
in aqueous solutions, for example, metal carbonates or sodium
phosphate, may be used also without addition of stronger bases, but
this is not advantageous because the reaction time is extended. If
a transition gradient is formed, it is limited to such a thin layer
that the optical properties of lens are not perceptibly affected
but causes the perfect bonding which is not damaged even at high
difference of swelling.
Another advantage of a very thin strongly swellable surface layer
is the reduced coefficient of friction between the lens and eye
tissue, so that the lens assumes rapidly and spontaneously the
prescribed centric position given by the geometry. This position is
stable, because the lens instantly returns to it after any
short-term displacement. The strongly swollen surface layer also
protects the lens from deposition of proteins and other less
transparent particles on the surface of the lens, so that the lens
remains permantly transparent. This fact is particularly important
for intraocular lenses.
The processing is advantageously carried out at temperature above
50.degree. C., at best around 100.degree. C., where the reaction
time is very short. The upper limit is the temperature at which
vapor bubbles could be formed inside the lens and damage the lens.
However, this limit is not achieved even near the boiling point of
salt solution, e.g. at 120.degree. to 130.degree. C. The processing
temperature of the lenses may be defined according to the invention
as a temperature between 50.degree. C. and boiling point of the
salt bath. The highly swellable exterior layer remains very thin
even at such high temperature, because the hydrogel does not swell
in the hot solution of salt but, on the contrary, it deswells if it
was previously swollen with water or aqueous liquid.
If the processing with the alkaline reacting solution of salt is
carried out at higher temperature under elevated pressure, the
formation of vapor bubbles in the hydrogel is reliably avoided.
However, suitable results can be reliably attained even by
processing of the lenses at atmospheric pressure.
EXAMPLE 1
A dry intraocular lens from the lightly crosslinked poly-HEMA is
immersed into aqueous solution containing 5 wt. % of sodium
hydroxide and 50 wt. % of potassium carbonate at the temperature of
solution 110.degree. C. for 5 minutes. The lens is then rinsed and
allowed to swell to equilibrium in distilled or deionized water.
The resulting lens contains 70 to 98% of water in its surface layer
which is 20 to 30 .mu.m thick, whereas the swelling of bulk of the
lens remains 30 to 40% as originally. The swelling capacity of
surface layer decreases to 60 to 65% by immersion into physiologic
saline, i.e. it is still at least 50% higher than of the original
hydrogel. The surface of lens is substantially smoother and softer
than before processing, optical properties remain unchanged.
EXAMPLE 2
A contact lens from the lightly crosslinked poly-HEMA, which is
swollen with water to equilibrium, is immersed for 5 minutes into a
saturated solution of Na.sub.2 SO.sub.4 containing 10% of NaOH and
heated to 100.degree. C. The lens is then rinsed with distilled
water. The result attained is practically the same as in example
1.
EXAMPLE 3
The procedure according to example 1 is repeated with the
distinction that a lens swollen with water and saturated solution
of potassium carbonate without addition of alkaline hydroxide is
used, temperature of salt bath is increased up to the beginning of
boiling, and the processing time is extended to 10 minutes. The
result is similar to that in example 1.
EXAMPLE 4
An intraocular lens from the copolymerization of 85% HEMA with 15%
of methyl methacrylate, crosslinked with 0.5% of ethylene glycol
dimethacrylate, was used in the procedure according to example 1.
The formed high-swelling surface layer remained transparent, while
immersion of the same lens into a 5% hot sodium hydroxide solution
caused a white cloudiness and the saponification affected the whole
depth of lens without formation of a sharply limited partially
saponified surface layer.
* * * * *